Variable pulley transmissions for transferring torque from an input or drive shaft to an output or driven shaft have been used for some time. In these transmissions, a first pulley constructed of a pair of flanges, at least one of which is conical, is mounted on the input shaft such that at least one of its flanges is axially movable with respect to its other flange. A second, similarly constructed and adjustable pulley is mounted on the output shaft. A flexible belt connects the two pulleys to transfer torque therebetween when the input shaft is driven. As the effective diameter of one pulley is changed, the effective diameter of the other pulley is changed in the other direction and, the drive ratio between the input and output shafts is adjusted in a smooth, continuous manner.
Automotive engineers have long recognized that the maximum operating efficiency of the engine could be achieved if the transmission could be controlled by adjusting to different loads and speed ratios, such that the engine is maintained and operated at its maximum efficiency operating conditions. This has not been possible when a conventional geared transmission is teamed with an engine. In the conventional geared transmission, the drive ratio is adjusted in discrete steps, rather than continuously. Accordingly, efforts have been directed to the use of a continuously varible transmission (CVT) of the type described above. The efforts have resulted in the production and marketing in Europe of the DAF passenger car, using flexible, continuous rubber belt to drivingly interconnect the pulleys. Rubber belts have been considered to be inferior to metal belts because of various adverse conditions under which they must operate. More recently, Fiat and Volvo have produced automobiles incorporating CVT's using respectively, metal belts and rubber belts. Some of the efforts to produce metal belts which are durable, relatively quiet in operation, and also economical to market, are described in the patent and other literature.
Flexible metal belts for use in CVT's are generally of two varieties, those referred to as "push" belts and those referred to as "pull" belts. Push belts are currently being used in the Fiat automobile's CVT. An example of a push belt is described in Van Doorne et al., U.S. Pat. No. 3,720,113 and an example of a pull belt is described in Cole, Jr., et al., U.S. Pat. No. 4,313,730. The Van Doorne et al. belt comprises an endless carrier constructed of a plurality of nested metal bands and an endless array of generally trapezoidal (when viewed from the front) load blocks encircling the carrier and longitudinally movable therealong. Each block has edge surfaces engaging the pulley's flanges of a pulley transmission to transmit torque between the pulleys. The pull belt of Cole, Jr. et al., utilizes an endless chain as the carrier, the sets of links of which are pivotably interconnected by pivot means. Load blocks, similar to those of Van Doorne et al., encircle the links; however, the load blocks are contrained against longitudinal movement along the chain by the pivot means.
Another example of a pull belt is shown in Ledvina, U.S. Pat. No. 4,569,671 which utilizes a chain-belt comprising a plurality of interleaved sets of links and load blocks associated therewith. Each link is defined by toes, the toes of each link being defined by parallel inside flanks joined by a crotch. A load block is received between the inside flanks and extends around the links. A hardened insert is located between the links and the blocks to protect the links and improve the durability of the chain.
The push belt as described above is relatively expensive to manufacture and must be installed and/or replaced as a complete endless loop. Thus, disassembly of at least part of the pulley transmission is required, not only for the initial assembly, but also for replacement of the push belt due to failure of one or more load blocks or one or more of the carrier bands.
The pull belt offers a less expensive alternative to the push belt. No precise matching of carrier parts is required. The belt can be assembled with a finite length, positioned around the pulleys, and the ends then connected by a pivot member. Thus disassembly of the pulleys is not required in either for initial installation or replacement of a belt.
Aside from costs, a major concern of automotive engineers is noise generation by drive belts for pulley transmissions. Noise of a mixture of frequencies is less objectionable to humans than noise of pure frequencies. Currently an evaluation used by some automotive engineers is to rate noise generated by drive belts of the type described herein in a generally subjective manner by driving or riding in an automobile in which the belt is installed and listening to the generated noise. The noise is then rated on a numerical scale of 1 to 10 with the higher numbers indicating the less objectionable noise. Belts achieving a rating of about 6 and above are usually acceptable for use in automotive drives, and can be classified as being of commercial quality. Of course such belts must also be durable, so as to have a reasonable operating life.
Various ways have been suggested for constructing belts for use in a CVT which operate in such a manner to generate noise acceptable to humans, and a discussion of some of these ways will be found in the prior art. A description of some of the prior art follows.
U.S. Pat. No. 4,464,152 discloses a chain-belt that has sound damping means interleaved with load block laminations.
U.S. Pat. No. 4,516,964 discloses load blocks of different transverse widths, all of which contact the pulley flanges, but some at a different radial location on the pulley flanges from others, thus modifying the generated noise pattern.
U.S. Pat. No. 4,516,965 discloses some load blocks do not contact the pulley flanges, or some load blocks are missing or "skipped", to thus modify the generated noise pattern.
U.S. Pat. No. 4,516,963 discloses a random mixture of load block-pulley flange engaging areas to provide a pattern of random engagement thereof with the pulley flanges, and thus a modified generated noise pattern.
A suggested way to modify the generated noise pattern in a chain in which the pivot means drivingly contacts the pulley flanges is to provide a drive chain constructed of a mixture of links of different pitches, such as U.S. Pat. No. 4,344,761, issued Aug. 17, 1982.
U.S. Pat. No. 1,868,334, issued Jul. 19, 1923, teaches constructing a chain for use with sprockets which provides a mixture of distances between adjacent centers of articulation or a mixture of "effective pitches" in order to "break up rythmic vibrations that sometimes cause trouble in chain drives". The patent is silent as to whether or not this "trouble" is noise related.
The invention to be described herein relates to chain and chain-belts which are used to connect sprockets or pulleys of power transmissions. The invention finds particular use for connecting the pulleys of a continuously variable transmission, commonly known as a CVT. In the description which follows, reference will be made to chain, it being understood that this includes not only tooth chains, also known as silent chain, but also structures known as chain-belts, which comprise a carrier of connected chain links, pivot means connecting interleaved chain links and drive blocks. The invention is primarily applicable to that variety of chain-belt known as pull belts.